1. Field of the Invention
This invention relates to the chemical tieing of two layers of dissimilar polymeric material to each other.
2. Description of the Prior Art
It is well known, especially in the field of rocketry, that it is often desirable to bond two layers of dissimilar polymeric material together and that it is often difficult to obtain tight bonds between two dissimilar materials. For example, Paul H. Skidmore mentions this problem in U.S. Pat. No. 3,813,308 in connection with the bonding of a carboxy-containing rubber liner to an insulator in a rocket motor. Skidmore solves his problem by applying a coat of polyisocyanate to the rubber insulator (by treating the insulator with a solution of the polyisocyanate and allowing the solvent to evaporate), then applying a layer of uncured carboxy-containing rubber liner material to the polyisocyanate coated surface and finally, curing the liner material. As the layer of carboxy-containing rubber liner material cures, its carboxy groups apparently react with the isocyanate groups of the polyisocyanate and a strong bond is formed. However, this method has a drawback in that a strong bond between the polyisocyanate coating and the rubber insulator is lacking.
Difficulties in bonding dissimilar polymeric material together arise because of differences in surface energies. For example, if atoms from the two polymeric layers cannot get close to each other (perhaps because of large size disparities), van der Waals forces cannot be taken advantage of. Nor can hydrogen bonding be taken advantage of.